Linear amplifier with extra wide band pass characteristics



Nov, 23, 1937. N. E. LINDENBLAD 2,109,193

LINEAR AMPLIFIER WITH EXTRA WIDE BAND PASS CHARACTERISTICS Filed Nov. 21, 1934 N.E. LINDENBLAD Mg ATTORNEY Patented Nov. 23, 1937 PATENT OFFECE IJNEAR ABIPLIFIER WITH EXTRA WIDE BAND PASS CHARACTERISTICS Nils E. Lindenblad, Port Jefferson,

N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 21, 1934, Serial No. 754,038

6 Claims.

This invention relates to amplifiers of the thermionic or electron discharge tube type and in particular to amplifiers of the tube type in which one or more tubes are utilized, and in 5' which said tubes are connected in what is known as direct coupled circuits, which circuits are arranged and cooperate with sources of potential in such a manner as to insure linear amplification of a wide band of alternating current potentials or of direct current impulses of a frequency which may extend over a considerable frequency range.

The invention is of wide application in the radio art, since it is useful for amplifying and relaying purposes in general. It is particularly applicable to amplifying modulation frequencies either in telephony or telegraphy facsimile, or television and picture transmission.

The novel features of my invention have been pointed out with particularity in the claims appended hereto, as required by law.

The nature of my invention and the manner in which the same operates will be understood from the following detailed description thereof and therefrom when read in connection with the attached drawing.

In the drawing the single figure illustrates a preferred form of direct current amplifier of the alternating current or direct current impulse type, :by means of which most of the disadvantages found in systems known heretofore in the art are eliminated.

In carrying out my invention, I contemplate the use of a novel tube in a novel circuit. The tube I propose to use has two grids. The second or additional grid, however, is not arranged nor located as a screen grid. The second grid is, as shown diagrammatically in the drawing of nearly the samedimensions as the first grid and is 40 preferably intermeshed with the first grid. The potentials to be amplified are supplied from any source to points I and 2 and impressed on the input electrodes of tube 5. As shown, the initial tube may be of the type described above, and the two grids l and I2 may be tied together and utilized as one of the input electrodes connected with the source. In tube the grids l0 and I2 may be of the same size and may be intermeshed as shown, or may consist of the usual control grid and auxiliary grid. The anode of the first tube 5 may be connected as shown direct to the grid ll of the second tube 6. The anode l4 of tube 5 is charged positive through a resistance Rp connected with the terminal of a source of potential B. In this circuit, no attempt need be made to keep the plate voltage of one tube from entering the grid of the next tube, as has been the case in direct coupled amplifiers known in the art. The second grid l2 of the second tube 6 may be connected by way of a resistance Rx to the negative terminal of a source of potential 0. If now a negative potential is applied to the second grid l2 through the separate resistor Rx of high resistance, the direct current potentials on the two grids are caused to cancel each other; in other words, the high direct current potential on grid ll of the second tube 6, due to its close coupling to the plate M of the first tube 5, is opposed and cancelled by the negative potential from C which is applied to grid l2 of the second tube, which gn'd I2, is as stated above closely intermeshed with grid H and is of the same di mension.

The voltage of the second grid 12 may also be adjusted or varied so that the resultant direct current potential in the tube system from the two grids will form a suitable bias potential for the combined grid efiect. Additional tubes, one being shown at 7, may be coupled in cascade in the same manner in which the second tube 6 is coupled-to the first tube 5. The direct current potentials or alternating current potentials may as stated above be applied to the points I and 2 and the amplified energy may be taken from the points 3 aud t. Of course, the first tube in this cascade amplifier may be replaced by a triode.

In the circuit illustrated, the resistances shown may be replaced by chokes, or complex impedan'ce circuits, where the latter are preferable, and in showing resistances, applicant does not intend to limit himself to the same, since obviously chokes or complex impedances may be utilized in place of the resistances, where desirable, with- .out'departing from the spirit of the present invention.

What is claimed is:

1. In a device for relaying direct current potentials and alternating current potentials, a thermionic tube having an anode, cathode and control grid, and an auxiliary gridlike electrode of substantially the same size as said control grid mounted adjacent said control grid, a circuit connected between the control grid and cathode of said tube, said circuit including a source of potential which maintains said control grid positive relative to said cathode, means for applying the potentials to be amplified to said circuit, an output circuit connected between the anode and cathode of said tube, said output circuit including a source of direct current potential to maintain said anode positive relative to said cathode, and a source of potential connected between said auxiliary grid and the cathode of said tube to maintain said auxiliary grid negative relative to said cathode to compensate the effect of the positive potential on said control grid on the tube operation.

2. A device for relaying direct current potentials and alternating current potentials comprising a thermionic tube having an anode, cathode and control grid, an auxiliary gridlike electrode or" substantially the same size as said control grid, said control grid and grid-like electrodes being closely related physically but conductively separated, a resistance connected between said control grid and the cathode of said tube by way of a source of direct current potential which maintains said control grid positive relative to said cathode, means for applying the potentials to be amplified between the cathode and the control grid of said tube, an output circuit connected between the anode and cathode of said tube, said output circuit including a source of direct current potential to maintain said anode positive relative to said cathode, and a resistance and a source of potential connected between said auxiliary grid and the cathode of said tube to maintain said auxiliary grid negative relative to said cathode to compensate the effect of said positive potential on said control grid on the tube operation.

3. A device for amplifying direct current potentials and alternating current potentials comprising a thermionic tube having an anode, cathode and control grid, and an auxiliary grid electrode intermeshed with said control grid, a resistance connected between said control grid and the cathode of said tube, a source of potential connected with said resistance for maintaining said control grid positive relative to said cathode, means for applying the potentials to be amplified between the control grid and cathode of said tube, a resistance connected between the anode and cathode of said tube, said resistance being connected to a source of direct current potential to maintain said anode positive with respect to said cathode, an output circuit connected with said resistance, and a resistance and a source of potential connected between said auxiliary grid and the cathode of said tube, said last named source of potential maintaining said auxiliary electrode negative relative to said cathode to compensate the effect of said positive potential in said control grid on the operation of said tube.

4. A relay circuit comprising a thermionic tube having a cathode, a control grid, an auxiliary grid of substantially the same size as said control grid intermeshed with said control grid, said tube also having an anode, a circuit for applying potentials to be amplified to said control grid and cathode, a

biasing circuit including a source of potential for maintaining said control grid at a higher than normal positive potential relative to the cathode of said tube, and means for overcoming the effect of said high positive potential on said control grid including a circuit connecting said auxiliary electrode to the negative terminal of a source of potential, the positive terminal of which is connected to the cathode of said tube.

5. In a multi-stage relay of the direct coupled type, a thermionic tube having a control electrode and a cathode on which potentials to be relayed may be impressed, said tube also having an anode electrode, a second thermionic tube having a control grid, an auxiliary gri-dlike electrode adjacent said control grid, a cathode and an output electrode, a direct connection between the anode of said first named tube and the control grid of said second named tube, a connection including an impedance between said direct connection and the positive terminal of a source of potential the negative terminal or" which is connected to the cathodes of said tubes whereby said directly connected anode and control grid are maintained at a high positive potential, an output circuit connected with the output electrode and cathode of said second named tube, and means for neutralizing the effect of the positive direct current potential on the control grid of said second named tube including a circuit for maintaining said auxiliary electrode negative with respect to the cathode of said tube.

6. A multi-stage amplifier of the direct coupled type comprising a thermionic tube having a control electrode and a cathode on which potentials to be amplified may be impressed, said tube alsohaving .an anode electrode, a second thermionic tube having a control grid, an auxiliary grid of substantially the same size as said control grid, a cathode and an output electrode, a direct connection between the anode of said first named tube and the control grid of said second named tube, a resistance connected between said direct connection and the positive terminal of a source of potential the negative terminal of which is connected to the cathodes of said tubes whereby said directly connected anode and control grid are maintained at a positive potential relative to said cathodes, an output circuit connected between the output electrode and cathode of said second named tube, and means for neutralizing the eiiect of the positive direct current potential on the control grid of said second named tube comprising a circuit including a resistance connecting the negative terminal of a source of potential to said auxiliary electrode, said last named source of potential having its positive terminal connected to the cathode of said second tube.

NILS E. LINDENBLAD. 

